We produced 3 murine monoclonal antibodies (mAbs) against the HIV-1 proteins. These mAbs, namely CA-1, CA-2, CA-4, were IgG1 and all reacted with p24 on the HIV-1 Western blot. One of the mAbs, CA-4, also recognized p13, p21, p28, p29, p32, p39, p47, p55 on the Biotech/Du Pont HIV-1 Western blot strips and p24, p28, p29, p39, p47, p55, p68, p80, p96, p110 on the Bio-Rad strips. CA-4 did not react with H-9 cell lysate nor with other retroviral antigens such as HTLV-1 or HIV-2 proteins. The binding of CA-4 to HIV-1 proteins was not blocked by deglycosylation. All three mAbs reacted with recombinant DNA derived capsid protein (p24) of HIV-1. These results suggest that many proteins in the HIV-1 Western blot contain antigenic epitope(s) similar to that of p24.